Production of rutile titanium dioxide



Patented Jan. 10, 1950 PRODUCTION OF RUTILE TITANIUNI DIO XIDE

Lawrence E. Ross and Charles A. Tanner, Jr., Am herst, Va., assignors, by mesne assignments, to American Cyanamid Company, a corporation of Maine No Drawing. Application January 31, 1942,

' Serial No. 429,118

This invention relates to the preparation of rutile titanium dioxide by the calcination of an anatase precipitate under controlled conditions, and aims to provide novel and unusually effective seeds for such purposes, and novel method of preparing such seeds.

Titanium dioxide, within the thirty years since its introduction as a pigment, has made such rapid strides that it has become the outstanding white pigment used in the coating and allied industries; this popularity is due mainly to its whiteness, stability, high hiding power, higher tinting strength, and ready dispersibility in ve-' hicles. It is prepared largely by the hydrolysis, under carefully controlled conditions, of titaninum sulfate solutions containing iron, pre-' pared by digestion of ilmenite (a native ferrous titanate) with sulfuric acid, followed by reduction of all ferric iron to ferrous iron, removal 01 a part of the iron by crystallization as ferrous sulfate, clarification and adjustment of concentration; the hydrolysate is calcined, together with con ditioning agents, to produce the desired white pigment.

The titanium dioxide so produced has been predominantly of anatase crystal structure, one of the three crystal modifications (anatase, brookite, rutile) in which titanium dioxide occurs. The art has known that the rutile structure, on account of its higher refractive index, should have higher hiding power and tinting strengththan the anatase structure, but rutile titanium dioxide having better hiding power and tinting strength has not been available commercially because there has been no process for its pro duction at a cost comparable with that of pro-' ducing anatase.

It is well known that the uncalcined precipitate obtained by the hydrolysis of titanium sulfate has the crystal structure of anatase, which is further developed upon calcination as the combined Water and the combined and/or adsorbed acid are expelled. It is also known that the 1111-" calcined precipitate. obtained by the hydrolysis of titanium salts of monobasic' acids, such .as; for example, titanium chloride, has the crystal structure of rutile, which is further developed upon calcination. It is also known that the anatase structure obtained by the hydrolysis of titanium sulfate can be converted to rutile by v 1 continued calcination at a very .high. temperature. Such calcination, however, causes crystal rowth and discoloration, which results in a product undesirable for use as a; white pigment,"

13 Claims. (Cl. 23-202) from salts of monobasic acids is economically- No process in which the titaniuin is precipitated competitive with the sulfate process, largely lee-'- cause of higher acid cost and the corrosion prob j lems introduced by the use of these monobasicj acids.

In co-pending patent application Serial Num' ber 422,104, filed December 8, 1941, now aban--' doned, it is proposed to convert an anatase pre-- cipitate, obtained by the hydrolysis of titanium sulfate solution, to rutile, by first roasting the precipitate in the presence of an alkali metal salt," washing the roasted precipitate substantially free of alkali metal salt, and then calcining in thepresence of a small amount of a rutile seed con-" sisting of calcined titanium dioxide, having the crystal structure of rutile, or consisting of an" uncalcined precipitate obtained by the hy-f drolysis of an aqueous solution of a monobas'ic' acid compound of titanium. It is disclosed that the rutile seed may be added either prior to or after the roasting operation. 4 v In co -pending patent application Serial Number 422,082, filed December 8, 1941, now abandoned, it is proposed to convert an anatase pro-f cipitate, obtained by the hydrolysis of titanium sulfate solutions, to rutile, by calcining in the: presence of a small amount of an alkali metal compound and a small amount of a rutile seed consisting of calcined titanium dioxide having the crystal structure of rutile, or consisting of an uncalcined precipitate obtained by hydrolysis of an aqueous solution of a m'on'obasic acid com f pound of titanium.

We have now discovered that the rutile conversion can be obtained considerably more ef-' fectively by the use of a rutile seed prepared by treating an alkali metal titanate with limited quantities of a monobasic acid, such as hydrochloric acid.

We may prepare the alkali metal titanate from any source of titanium dioxide (e. g. rutile, il-" menite, hydrated precipitates obtained in theordinary manufacture of pigment TiOz, etc.) by the use of alkaline alkali metal compoundsin' known manner. w

In our preferred'procedure, an aqueous pulp ofi substantially pure hydrated titanium dioxide containi'ng a small 'amount'of combined and/or ad sorbed sulfuric'acid, obtainedby hydrolytic pre cipitation from "a titanium sulfate solution, is treated with an alkaline alkali 'metal compound such as sodium hydroxide, potassium hydroxide,- etc. The hydrated oxide is treated 'with'froml about one'part to about fiveparts by weight oii'; sodium hydroxide toone partpf anhydrous titanium dioxide, and heated for from about one hour to about six hours at a temperature of about 80 C. to 100 C. About one and one-half parts of sodium hydroxide is a preferred amount. Solid flake sodium hydroxide may be mixed. with, the concentrated aqueous pulp of the .liydrated titanium dioxide, and then heated without further agitation. A concentrated aqueous solution of so; dium hydroxide may be mixed with the hydrated titanium dioxide pulp, and heated while con; tinuously stirring. Depending upon the amount of sodium hydroxide used, andalsouponthe con-,- centration of the sodium hydroxide and; hydrated titanium dioxide mixture, the. temperature may vary considerably up to and above 100 C., even up to the fusion point, if desired. The reaction may be carried out under atmospheric conditionspr under pressure in an autoclave; under the latter conditions, the reaction mass remains fluid. .To

the sodium titanate thus formed, water, which may cause some hydrolysisof the titanate, and consequent formation of hydrated titaniumdioxide and/or other titanate or titanates, is added. The solids are washed by .decantation and then filtered and washed. The Washed solids contain, by analysis after calcination, about 85% titanium dioxide, andabout sodium oxide. No attempt is made herein to ascribe any definite composition to the original titanate. formed, nor to the solids remaining after treatment with water and washing.

a If; desired, the hydrated. titanium dioxide pulp may be treated with a suificient amount. of an alkaline compound, to react with the combined end/or adsorbed sulfuric acid, and then dilutedand washed. .to remove the. sulfate prior to treatment with an alkaline alkali metalv compound to tormatitanate- 1 The-washed solids are treated with hydrochloric acid in-suflicientquantity toneutra-lizethe sodium oxide, and in suffici entexcess for about to:.about .50% of theory for the formation of. titanium tetrachloride. About.2 5% of the theoretical quantity for titaniumv tetrachloride after neutralizing the sodium oxide ispreferred. .The hydrochloricacidslurry isv diluted with watenand boiledfor about one. hour. Nitric acid, or other monobasic .acids, may be. used. in place of hydrochloric acid., The amountof acid, used is ordi narilyinsufii'cient for complete solution .of tita's nium, although. pept'zation generally occurs. The titanium, however, during the boiling period, is. transformed to a desirable rutile; seed for. use in convertinganatase structure. to rutile structure during calcination. Some suchseeds prepared by us have shown by X-ray analysis substantially complete rutile structure.

If desired, the titanate may be treated directly with the monobasic acid, thus omitting the: water treatment. We prefer to use the water treatment, however; since it eliminatesa large amount of the: alkali metal-and. sulfate, and. thereby reduces the amount of: .monobasic: acid. .required-.. urther;-- more-,,; a. more active. seed isgenerally obtainedif' the alkali metal and sulfate are largely removed prior. to the monobasic acid treatment.

. Therutile seed thus .formedmay' beused. as such by mixing, with an uncalcinedi hydrated titaa nium dioxideprecipitat'e, obtained; .by hydrolytic precipitation from a titanium sulfate solutiorrat any stagein the process prior to the final wash: me before calcination, or itmay; be fiocculated by adjusting the slurry to apH of from about 4.5 7.5. by neutralizing with. an. alkaline reagent.- such; sodium carbonate, filtered, washed. sub

stantially free of chlorides, and then mixed with an uncalcined hydrated titanium dioxide precipitate, obtained by hydrolytic precipitation from a titanium sulfate solution at any stage in the process prior to .calcination. g

. Our special rutile seed is extremely finely divided, which probably accounts for its exceptional activity. By its use as a seed, even in relatively finial] amounts, substantially complete conversion to rutile may be obtained under ordinary calcination conditions.

3 ,Theamount of rutile seed used may vary within wide limits. W hile' in general we prefer to use about. 5%, based upon the total weight of the r titanium dioxide calcined, smaller and larger percentages maybe used. Even as little as 1% or less is effective. Obviously there is no upper limit;

..The.actual amount of rutile seed used depends upon the amount of riitile conversion desired, and also uponthe desired other properties of the finishedpigment, such as'color and softness. The use 9f; 5% or more seed induces conversion to rutile at-a lower temperature or in a shorter time or; both, and thereby produces a pigment oi rutile structure Which has a. color higher in total brightness. and which disperses more readily when ground in vehicles.

It is desired toplace no limit upon the rutile conversion obtained. For certain purposes, relatively small conversion may be desired, and in other cases a substantially complete conversion may be desired. Forexample, it may be desirable to produce a pigment containing 15% rutile 1 and-35% anatase, or a pigment containing rutile and.10% anatase. The hiding power and tinting strength; of the pigment produced accordingto. our process increases proportionately as the conversion to rutile increases. Asmall amount. of. an iron salt, such as ferric ammonium. sulfate, or a small amount of copper salt. suchas copper sulfate, which salts decompose and. form the oxides of the metals upon calcination, may be added at some stage prior to calcining to prevent bluing Or grayin of the color .oflthe pigment during calcination. The preferred amount of iron is from about .01% to about. .03.%-, calculated as FezOs, and based upon theweight of the titanium dioxide. If the uncalcined hydrated titanium dioxide already contains an appreciable amount of iron, the amount addediscorrespondingly less than the .Ol% to 0 3:% ,.-so-.that-the calcined pigment will contain from 01% to 113%- F8203. The preferred amount of copper is from .0004% to .002%, calculated as CuO.

Detailed methods for the preparation of our rutile seedare given in Examples 1, 2 and 3.

Erample 1 .An'aqu'eous pulp of substantially pure hydrated titanium dioxide, containing a small amount of combinedand/or'adsorbed sulfuric acid, obtained byhydrolytic precipitation from a titanium sulfate solutiomnnd containing grams of titanium dioxide, is. diluted. withwater to about 30%,

calcined solids content. -To this aqueous slurry 2-5. washed. substantially free of sulfates. lhe filter cake is slurried in 185 cc. of commercial B. hydrochloric acid, diluted with one liter of water, and boiled at constant volume for about one hour.

Example 2 An aqueous pulp Of substantially pure hydrated titanium dioxide, containing a small amount of combined and/ or adsorbed sulfuric acid, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 100 grams of titanium dioxide, is diluted with Water to about calcined solids content. To this aqueous slurry is added 150 grams of flake sodium hydroxide, while stirring continuously. The mixture is then heated for about two hours at a temperature of about 85 C. to 90 C., while stirring continuously, and at a constant volume. The titanate thus formed is diluted to about 1 /2 liters with water, Washed twice by decantation, then filtered and washed substantially free of sulfates. The filter cake is slurried in 185 cc. of commercial 20 B. hydrochloric acid, diluted with one liter of water, and boiled at constant volume for about one hour. The seed slurry is cooled to C., and

-. adjusted to a pH of 6.0 by the addition of about 340 cc. of 20% solution of sodium carbonate. At this pH the seed is sufficiently fiocculated to be filtered. It is filtered and washed substantially free of sodium and chloride ions.

Example 3 An aqueous pulp of substantially pure hydrated titanium dioxide, containing a small amount of combined and/or adsorbed sulfuric acid, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 100 grams of titanium dioxide, is diluted with water to about 30% calcined solids content. To this aqueous slurry is added 150 grams of flake sodium hydroxide, while stirring continuously. The mixture is then heated for about two hours at a. temperature of about C. to 0., while stirring continuously, and at a constant volume. The titanate thus formed is diluted to about 1 liters with water, washed twice by decantation, then filtered and washed substantially free of sulfates. The filter cake is slurried in cc. of commercial 42 B. nitric acid, diluted with one liter of water, and boiled at constant volume for about one hour.

Having described our invention and given examples illustrating methods for preparing the rutile seed, we now give examples illustrating the conversion of anatase structure to rutile structure.

Example 4 product is milled and slurried in sufficient water.

to give a pulp containing 15% solids. 5 cc. of commercial 20 B. hydrochloric acid are added, and the solids are filtered out and washed substantially free of sulfates. The washed filter cake is then dried and calcined by slowly raising the.

temperature from about 300? C. to about 975" C.

75 The calcinedpigment contains by X-ray anal-Q.

a tially complete.

6 during about five hours, and then holding at a temperature of about 950? C. to about 1000 C. for about two hours.

The transformation to rutile, as determined by X-ray analysis, has been substantially complete. The tinting strength of the hydroclassified and dry milled pigment is 1720.

Tinting strength evaluations are based upon an arbitrary scale in which present commercial titanium dioxide of anatase crystal structure has a value of 1250.

Example 5 A thoroughly washed aqueous pulp of an hydrated titanium dioxide precipitate, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 200 grams of titanium dioxide, is mixed with 0.24 gram of ferric ammonium sulfate containing .04 gram of ferric oxide, and with 4.0 grams of potassium carbonate. The mixture is dried and roasted for one hour at a temperature of about 850 C.

The roasted product is milled and slurried in water. 85 grams of the hydrochloric acid suspen--' sion of Example 1, containing 6 grams of titanium dioxide, are added. The mixture is filtered and the filter cake is washed substantially free of alkali metal salts. The filter cake is then dried and calcined by slowly raising the temperature from about 300 C. to about 975 C. during about five hours, and then holding at a temperature of about 975 C. to about 1000 C. for about two hours. The transformation to rutile, as determined by X-ray analysis, has been substan- The tinting strength of the hydroclassified and dry milled pigment is 1720.

Eeample 6 A thoroughly washed aqueous pulp of an hydrated titanium dioxide precipitate, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 200 grams of titanium dioxide, is diluted with water to a calcined solids content of 20%, and mixed with 85 grams of the hydrochloric acid suspension of Example 1, which dried and calcined by slowly raising the temperature from about 300 C. to about 975 C. during about five hours, and then holding at a temperature of about 975 C. to about 1000 C. for about four hours.

The calcined pigment contains by X-ray analy-' sis about 90% rutile. The tinting strength of the hydroclassified and dry milled pigment is 1700.

Example 7 4 A thoroughly washed aqueous pulp of an hydrated titanium dioxide precipitate, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 200 grams of titanium dioxide, is mixed with grams of the neutral-;

ized, filtered and washed seed of Example 2 containing 10 grams of titanium dioxide, and with a concentrated aqueous solution containing 0.42 gram of potassium carbonate and calcined for about two hours at a temperature of about 975 C. to about 1000 C.

amuse ysi's; about 90%- rutile; The-tintingnstrength or the hydrociassified and: dry" milled pigmentis 1700. The color of the product is not quite as good as that of the products obtainedin' Examples 4; 5 and 6, due to theomission of the iron addition.

Example 8 A thoroughly washed aqueous pulp of. an hydrated titanium dioxide precipitate, obtained by hydrolytic precipitation from a titanium sulfate solution, and containing 200 grams of titanium dioxide, is diluted with water to a calcined solids content of and mixed with 145 grams of the nitric acid suspension of Example 3,- containing 10 grams of titanium dioxide. The mixture is filtered, and the filter cake is washed substantially free of nitrates. The filter cake is then mixed with 0.24 gram of ferric ammonium sulfate containing 0.04 gram of ferric oxide, and'with a concentrated aqueous solution containin 0.42 gram of potassium carbonate; dried and calcined by slowly raising the temperature from about 300 C; to about 975 C. during about five hours, and then holding at a temperature of about 975 C; to about 1000 C. for about three hours.

The transformation to rutile, as determined by X-ray analysis, has been substantially complete; The tinting strength of the hydroclassiiied pigment is 1720. I

While a rather definite calcination schedule is" indicated in the examples, this schedule may be varied considerably. In actual commercial oper ation the calcin'ation may be continuous through a rotating horizontal kiln, which is heated at the discharge end, and in which therefore there is a gradual temperature change from one end of the kiln to the other.

Our calcined pigment, obtained in accordance with any of the modifications of the. invention, may be either simply dry milled 'or wet milled, by droclassified, treated with the usual reagents, filter ed, dried and disintegrated in accordance with the present known procedures for producing the commercial titanium dioxide pigments having the anata'se crystal structure.

Our finished pigment has many desirable properties, such as good resistance to chalking, excel lent resistance to discoloration in white baking 5 enamels, etc., but is characterized. in the main by its exceptional hiding power and tinting strength. The hiding power and tinting strength of the product in which the conversion torutile has been substantially complete is in the neighborhood of 40% higher than that of present commercial titanium dioxide having the anatase crystal structure. When the conversion to rutile has been less, the advantage in hiding power and tinting strength is correspondingly less.

We claim:

1. A process for preparing a rutile seeding agent, which comprises treating an alkali metal titanate with 'a monobasic acid in suflicient amount to completely convert the alkali metal content to the salt ofthe inonobasic acid and to theoretically convert about 20% to of the titaniiun content to the salt of the monoba'sic acid, and boiling the resultant mixture for about one hour, whereby the titanium content is substantially converted to 'a rutile conversion seed showing rutile structure upon X-rayanalysis.

2. A seeding agent for use in converting to rutile anatase precipitates obtained-by the l ly- .dr'olysis of titaniruh slur-admissions, ens seed- .with a monobasic acid in sufiicient amount to completely convert the alkali metal content to the salt oftlie monobasie" acid and to theoretically convert about 20% re 50 of the titanium content to the salt of the monobasic acid, and boiling use resultant mixture for about one hour, whereby the titanium content is substantially converted to a rutile conversion seed showing rutile structure upon X ray'analysis.

4; A process for preparing a rutile seeding agent, which comprises treating asodium titanate with hydrochloric acid in suiiicient amount to completely convert the alkali metal content to the salt of the mono-basic acid and to theoretically convert about 20% to 50% of the titanium content to the salt of the mono-basic acid, and boiling the resultant mixture for about one hour, whereby the titanium content is substantially converted to a rutile conversion seed showing rutile struc' ture upon X-ray analysis.

5. A process for producing rutile seed for use in the production of titanium dioxide, having rutile crystal structure, which comprises treating hydrated titanium dioxide obtained by hydrolyti'c precipitation from titanium sulfate solutions, with an alkaline sodium. compound to form a sodium titanate, washing the titanate relatively free of sulfate, and treating the titanate with hydrochloric acid in 'sufii'ci'ent amount to completely convert the alkali metal content to the salt of the m'onobasic acid and to theoretically convert about 20% to 50 of the titanium content to the salt of the monobasi'c acid, and boiling the resultant mixture for aboutonehour, whereby the titanium content is substantially converted to a rutile conversion seed showing rutile structure. upon X-ray analysis.

6, The method of producing rutile titanium dioxide from a precipitate which ordinarily calcines to anatase, which comprises calcining the precipitate in admixture with significant quantitles of a dispersion of a rutile seed prepared by treatin an alkali metal. titanate with a monobasic acid in sufiicient amount to completely convert the alkali metal content to the salt of the monobasic acid and to theoretically convert about 20% to- 50% of the titanium content to the salt of the monoba'si'c acid, and holding the resultant mixture for a period of time at an elevated temperature, whereby the titanium content is substantia-lly converted to a rutile seed, the calcin'ation being performed. at a temperature not exceed-ingabbut 1000 G;

'1. The method of producing rutile titanium dioxide from a precipitate which ordinarily calcines to anatase, which comprises calcining the precipitate-in adrruxture with significant quantities of a dispersion of a rutil'e'seed prepared by treating a sodium titanate with hydrochloric acid in sui'hcient amount to completely convert the alkali metal content to the salt of the monobasic acid and to theoretically convert about 20% to 50% of thetitaniurn contentto the salt of the mcncbasic acid, 'andholding the resultant" mixture for a period 'of time at an elevated temperature, whereby the titanium content is substantially converted to a rutile seed, the calcination being performed at a temperature not exceeding about 1000 C.

8. The method of producing rutile titanium dioxide from a precipitate which ordinarily calcines to anatase, which comprises calcining the precipitate in admixture with significant quantitles of dispersion of a rutile seed prepared by treating an alkali metal titanate with a monobasic acid in sufficient amount to completely convert the alkali metal content to the salt of the monobasic acid and to theoretically convert about to 50% of the titanium content to the salt of the monobasic acid, and holding the resultant mixture for a period of time at an elevated temperature, whereby the titanium content is substantially converted to a rutile seed, the calcination being carried out in the presence of a small amount of a compound of the group of metals consisting of iron and copper, the calcinatin being performed at a temperature not exceeding about 1000 C.

9. The method of producing rutile titanium dioxide from a precipitate which ordinarily calcinesto anatase, which comprises calcining the precipitate in admixture with significant quantities, of the order of 1% or more, based on calcined solids content, of a rutile seed prepared by treating an alkali metal titanate with a monobasic acid in sufficient amount to completely convert the alkali metal content to the salt of the monobasic acid and to theoretically convert about 20% to 50% of the titanium content to the salt of the monobasic acid, and holding the resultant mixture for a period of time at an elevated temperature, whereby the titanium content is substantially converted to a rutile seed, fiocculating and filtering ofi" the resulting titanium compound and washing it substantially free of alkali metal and monovalent acid ions, the calcination being performed at a temperature not exceeding about 1000 C.

10. The method of producing rutile titanium dioxide from a precipitate which ordinarily calcines to anatase, which comprises calcining the precipitate in admixture with significant quantities, of the order of 1% or more, based on calcined solids content, of a rutile seed, prepared by treating a sodium titanate with hydrochloric acid in sufiicient amount to completely convert the alkali metal content to the salt of the monobasic acid and to theoretically convert about 20% to 50% of the titanium content to the salt of the monobasic acid, and holding the resultant mixture for a period of time at an elevated temperature, whereby the titanium content is substantially converted to a rutile seed, fiocculating and filtering ofi the resulting titanium compound and washing it substantially free of alkali metal and monovalent acid ions, the calcination being performed at a temperature not exceeding about 1000 C.

11. A solid, finely divided seed for accelerating the conversion to a rutile titanium dioxide pigment of a titanium dioxide precipitate which ordinarily calcines to anatase which consists essentially of the product obtained by treating an alkali metal titanate with a monobasic acid in sufficient amounts to completely convert the alkali metal content thereof to the salt of the monobasic acid and to theoretically convert 20% to 50% of the titanium content to the salt of the monobasic acid, boiling the resulting mixture for about one hour to bring about conversion of the titanium content to a rutile .conversion seed, fiocculating and filtering off the resulting titanium compound and washing it substantially free of alkali metal and monovalent acid ions.

12. A process for preparing a rutile seeding agent which comprises treating an alkali metal titanate with a monobasic acid in sufficient amount to completely convert the alkali metal content of the said titanate tothe salt of the monobasic acid and to yield a suspension which is strongly acid, and then heating said suspension for a period of time at an elevated temperature sufiicient to develop the seeding properties thereof.

13. A process for preparing a rutile seeding agent which comprises treating an alkali metal titanate with a monobasic acid in suflicient amount to completely convert the alkali metal content of said titanate to the salt of the monobasic acid and to theoretically convert about 20% to 50% of the titanium content to the salt of the monobasic acid, and then heating said suspension for a period of time at an elevated temperature sufiicient to develop the seeding properties thereof.

LAWRENCE E. ROSS. CHARLES A. TANNER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,697,929 Ryan Jan. 8, 1929 1,922,328 Rhodes Aug. 15, 1933 1,931,682 Rhodes Oct. 24, 1933 1,932,087 Richter Oct. 24, 1933 2,029,881 Little Feb. 4, 1936 2,286,882 Von Bechowsky et al. June 16, 1942 2,292,507 Brooks Aug. 11, 1942 2,301,412 Keats et a1 Nov. 10, 1942 2,303,306 Tillmann Nov. 24, 1942 FOREIGN PATENTS Number Country Date 149,316 Great Britain June 16, 1921 405,669 Great Britain Feb. 12, 1934 463,996 Great Britain Apr. 8, 1937 533,227 Great Britain Feb. 10, 1941 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, Volume VII, pa e 39. 

1. A PROCESS FOR PREPARING A RUTILE SEEDING AGENT, WHICH COMPRISES TREATING AN ALKALI METAL TITANATE WITH A MONOBASIC ACID IN SUFFICIENT AMOUNT TO COMPLETELY CONVERT THE ALKALI METAL CONTENT TO THE SALT OF THE MONOBASIC ACID AND TO THEORETICALLY CONVERT ABOUT 20% TO 50% OF THE TITANIUM CONTENT TO THE SALT OF THE MONOBASIC ACID, AND BOILING THE RESULTANT MIXTURE FOR ABOUT ONE HOUR, WHEREBY THE TITANIUM CONTENT IS SUBSTANTIALLY CONVERTED TO A RUTILE CONVERSION SEED SHOWING RUTILE STRUCTURE UPON X-RAY ANALYSIS. 